Several solutions have been implemented to attain this aim. The patent EP-A-0 110 804 describes one embodiment example comprising one rotary gasket mounted on a shaft associated with one element forming a valve.
Another solution consists of mounting on a shaft at the level of the partition passage an equipped housing comprising an oil extraction gimlet cooperating with the external surface of the shaft and a carbon, graphite or amorphous carbon ring, possibly segmented, directly mounted and pre-assembled on the housing. This solution facilitating implementation does, however, have the drawback of rendering the device heavy and increasing costs.
Another solution described in the patent No 89 03019 consists of providing at the level of the housing an oil extraction gimlet cooperating directly with the shaft and of using an integrated gasket consisting of a segmented carbon ring forming the radial joint.
The segments are rendered integral by means of an elastic ring housed in one peripheral throat of these segments and, on their dynamic sealing face, comprising discharge cavities whose purpose is to limit the specific pressure between the carbon joint and the functioning rotor. The integrated gasket also comprises a retention ring connected to the housing by locking means.
The radial joint constituted by the segmented carbon ring is extremely effective when the pressure of the air chamber is greater than that of the oil chamber. Imperviousness is improved by adding the additional system constituted by the oil extraction gimlet, but remains insufficient for certain cases of operation.
In fact, the play existing between the gimlet and the shaft to too large so as to ensure a sufficient extraction of oil as it has been established that all the oil nevertheless manages to traverse this gimlet and goes past the carbon joint so as to reach the air chamber.
Now, this play is brought about by the functioning of the motor and thus allows for functioning at both high and low rates.
The imperviousness system described in this patent does not therefore make it possible to obtain full imperviousness for all the possible operating configurations of the motor.